Construction sites require foot and wheeled traffic for months before the exterior landscaping has been completed. The foot traffic can track mud and detritus into the construction site.
Wheeled vehicles can get stuck in mud or against discarded construction material. Some construction sites put down plywood which can be a tripping hazard at the overlaps.
Some nations or regions require handicap access to buildings while the landscape is under construction or otherwise do not have sidewalks.
Others may be in need of a walkway immediately and can't wait for setting up forms and drying of concrete.